\(\mathbf {D}^{(l+1)} = \arg \min _\mathbf {D} \frac{1}{2} \Vert \left( \mathbf {Y} - \mathbf {F} \mathbf {H}^{(l)} \right) - \mathbf {FD} \Vert _2^2 + \lambda _4 \Vert \mathbf {D} \Vert _{2,1}\) , solved by the M-FOCUSS algorithm [1]};
